Regional distribution of erosion rates over the Japanese Islands

Fujiwara, Osamu; Sanga, Tomoji*; Omori, Hiroo*

Regional distribution of erosion rates has been studied to clarify the long-term stability of the geological environment in Japan. The regional distribution of erosion rates should be estimated to predict long-term geomorphological changes. This research is to estimate the distribution of erosion rates over the Japanese Islands based on the relationship between the sediment delivery rates to reservoirs and the dispersion of altitude of the drainage basins. The relationship between erosion rate E(mm/y) and dispersion of altitude D(m) of drainage basins is expressed by E=0.000044 D with a correlation coefficient of 0.94. This equation was used to calculate the denudation rate for each 6 km 6 ㎞ area of the Japanese Islands using a "digital map 50 m grid". The denudation rates are, highest in the central Japanese mountains ( 3-5 mm/y), moderate in the outer belt of Southwest Japan, the inner belt of Northeast Japan and Hokkaido ( 2-3 mm/y), and lowest in the inner belt of Southwest Japan, outer belt of Northeast Japan and central Hokkaido ( 1 mm/y). These regional characteristics are closely related to the distribution of Quaternary uplift rates, which caused the regional differences in surface topography.